1. Field
The present invention relates to a flat fluorescent lamp for a display apparatus, and more particularly to flat fluorescent lamp for a display apparatus, capable of improving luminance uniformity without having to increase an initial operation voltage.
2. Background
There are two types of display apparatus: an emissive display apparatus and a non-emissive display apparatus. A liquid crystal display LCD is the typical non-emissive display apparatus, and it requires backlighting from behind the liquid crystal elements to display characters, images, and so forth.
There are basically two mechanical implementations of a backlight: edge lighting and surface lighting. The edge lighting approach uses one or more lamps, typically cold cathode fluorescent lamps (CCFL), at the edge of the display. A thin light guide distributes the light from the lamps evenly across the display surface. The surface lighting approach has a cavity configuration with cold cathode fluorescent lamps (CCFL) behind the LCD panel.
The surface light approach is generally superior in luminance, but inferior in luminance uniformity. The edge light approach is generally inferior in luminance, but superior in luminance uniformity.
FIG. 1 is a perspective view illustrating a disassembled structure of a conventional flat fluorescent lamp. FIG. 2 is a plan view illustrating the conventional flat fluorescent lamp. The conventional florescent lamp 100, as shown in FIGS. 1 and 2, is manufactured by assembly of a first substrate 110 and a second substrate 120. One or more channels 111 having the same cross-sectional area, are formed at regular intervals on the first substrate 110. The second substrate 120 has a flat surface. One or more discharge spaces are formed by assembly of the first substrate 110 and the second substrate 120.
A sealant 130 is dispensed along an edge of the second substrate 120 to create a joint between surfaces of the first substrate 110 and the second substrate 120 to assemble the first substrate 110 and the second substrate 120. The assembly of the first substrate 110 and the second substrate 120 results in channels 111 being physically separated from each other, thereby forming a plurality of discharge spaces. A discharge gas is introduced into the channels 111, i.e., the discharge spaces.
Electrodes 140 in the form of a belt are formed on both ends of upper and lower sides of the assembly of the first substrate 110 and the second substrate 120. A voltage is then applied to the electrodes 140. Each of the channels 111 includes an electrode section 111a where the electrodes 140 are formed, and an emitting section 111b where light is emitted. When a voltage is applied to the electrodes 140, electric discharges occur within the discharge spaces, thereby emitting light from the emitting sections 111b. 
Each of the channels of the conventional flat fluorescent lamp 100 has electrode sections 111a and emitting sections 111b whose cross-sectional areas are the same. However, an inside space of the electrode sections 111a is smaller than an inside space of the emitting sections 111b. Because the inside space of the electrode sections is smaller, there are fewer electrons available to excite, and it takes a relatively long time or a relatively high voltage to get the flat fluorescent lamp 100 to initially light up. Thus, it is necessary to increase an initial discharge voltage to reduce the initial operating time for the flat fluorescent lamp 100. However, increasing in the initial discharge voltage results in excessive collisions between electrons within the channels 111, thereby shortening a life of the flat fluorescent lamp.
The electrode sections 111a are subject to transformation due to the high heat generated when a voltage is applied to the electrodes 140. Transformation of the electrode sections 111a brings about separation of the contact surfaces of the first substrate 110 and the second substrates 120 along the joint. Thus, the discharge gas within the channels may mix. Accordingly, luminance and luminance uniformity can deteriorate.
Uneven luminance of the flat fluorescent lamp may also occur due to temperature differences between the channels. The channels positioned at the middle of the fluorescent lamp are in a range of relatively high temperature and luminance is therefore high. The channels positioned at the sides of the fluorescent lamp are in a range of relatively low temperature and luminance is therefore low. The higher heat at the center results from positioning of a component such as an inverter on the middle of the back side of the fluorescent lamp, and/or from convection of the discharge gas between the channels with the flat fluorescent lamp in the upright position.